As a result of the widespread use of computers and other microprocessor-based equipment, the quality of power at sites having such equipment has become increasingly important. Utility companies deliver electric power to customer sites as an alternating current (AC) voltage through a secondary power distribution system. Various distribution system and environmental factors, however, can cause power line anomalies, such as spikes, surges, sags, transients or other distortions, and can cause blackouts, brownouts, or other distribution system problems that greatly affect the quality of power received by the customer at a site. Electronic equipment, such as computers and other equipment, are susceptible to damage and/or a faulty operation as a result of power line anomalies and other poor power quality conditions.
Power monitoring equipment has been used to monitor the power quality at a site that uses electronic equipment. Power monitoring equipment may be used to record voltage data and to detect and identify power events such as spikes, sags, surges and transients. When using conventional power monitoring equipment, however, certain low frequency events may not be detected and/or identified. One example of such a low frequency event is a voltage transient caused when a discharged power-factor-correction (PFC) capacitor is switched across a line. Another example may be a voltage anomaly caused by large highly capacitive or inductive loads, e.g., HVAC, motors, etc. Although such low frequency event may be low in amplitude, they may be high in distortion and should not be ignored.
Users of existing monitoring equipment may expect to detect such low frequency events when detecting sags and swells but may overlook such events because the voltage distortion is sub cycle. Low amplitude low frequency anomalies have also been discounted and not considered to be a concern. Some existing standards, such as the CBEMA curve, classify voltage transients using peak voltage as a percentage of nominal voltage versus time. Although these existing standards may be used to identify high frequency transients, low amplitude low frequency events may not be effectively identified when using such standards.